Actions of Interferons on Macrophages

Mice intravenously infected with an immunizing dose of the gram- positive bacterium, Listeria monocytogenes, produced circulating interferon IFN during the inductive phase of the anti-Listeria immune response. In addition to inducing IFN, the Listeria also dramatically altered the hosts responsiveness to IFN inducing agents. Within 24 hours of infection, mice acquired a 50-fold greater than normal capacity to produce the alpha andor beta IFN classes IFN alphaBeta following intravenous injection of endotoxin. Serum IFN alphabeta levels peaked by 2 hours after which, high levels of gamma IFN IFN gamma were detected in the sera of Listerian-infected animals given the B cell mitogen. Similar studies carried out with the interferon inducing agent polyinosinic-polycytidylic acid Poly I.Poly C which, like endotoxin, induces peak levels of serum IFN 2 hours after intravenous injection, revealed that 24 hour infected mice produced only 4-8 times more IFNaplhbeta than non- infected mice. However, unlike endotoxin, PolyI.PolyC did not elicit IFN gamma synthesis in Listeria-infected animals.